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$set (aggregation)

The $set operator updates an existing field or creates a new field with the specified value if it does not exist. One or more fields listed are updated or created. The dot notation is used to update or create nested objects.

Syntax

{
  "$set": {
    "newField": <expression>,
    ...
  }
}

Parameters

Parameter Description
newField The name of the field to update or create
expression The expression that defines the value of the new or updated field

Examples

Consider this sample document from the stores collection in the StoreData database.

{
    "_id": "0fcc0bf0-ed18-4ab8-b558-9848e18058f4",
    "name": "First Up Consultants | Beverage Shop - Satterfieldmouth",
    "location": {
        "lat": -89.2384,
        "lon": -46.4012
    },
    "staff": {
        "totalStaff": {
            "fullTime": 8,
            "partTime": 20
        }
    },
    "sales": {
        "totalSales": 75670,
        "salesByCategory": [
            {
                "categoryName": "Wine Accessories",
                "totalSales": 34440
            },
            {
                "categoryName": "Bitters",
                "totalSales": 39496
            },
            {
                "categoryName": "Rum",
                "totalSales": 1734
            }
        ]
    },
    "promotionEvents": [
        {
            "eventName": "Unbeatable Bargain Bash",
            "promotionalDates": {
                "startDate": {
                    "Year": 2024,
                    "Month": 6,
                    "Day": 23
                },
                "endDate": {
                    "Year": 2024,
                    "Month": 7,
                    "Day": 2
                }
            },
            "discounts": [
                {
                    "categoryName": "Whiskey",
                    "discountPercentage": 7
                },
                {
                    "categoryName": "Bitters",
                    "discountPercentage": 15
                },
                {
                    "categoryName": "Brandy",
                    "discountPercentage": 8
                },
                {
                    "categoryName": "Sports Drinks",
                    "discountPercentage": 22
                },
                {
                    "categoryName": "Vodka",
                    "discountPercentage": 19
                }
            ]
        },
        {
            "eventName": "Steal of a Deal Days",
            "promotionalDates": {
                "startDate": {
                    "Year": 2024,
                    "Month": 9,
                    "Day": 21
                },
                "endDate": {
                    "Year": 2024,
                    "Month": 9,
                    "Day": 29
                }
            },
            "discounts": [
                {
                    "categoryName": "Organic Wine",
                    "discountPercentage": 19
                },
                {
                    "categoryName": "White Wine",
                    "discountPercentage": 20
                },
                {
                    "categoryName": "Sparkling Wine",
                    "discountPercentage": 19
                },
                {
                    "categoryName": "Whiskey",
                    "discountPercentage": 17
                },
                {
                    "categoryName": "Vodka",
                    "discountPercentage": 23
                }
            ]
        }
    ]
}

Example 1 - Update an existing field

db.stores.updateOne({"_id": "8eefe8bd-5d6f-4038-90e8-05a8277637f0"}, {"$set": {"name": "Lakeshore Retail"}})

Example 2 - Update an existing field in a nested object

db.stores.updateOne({"_id": "8eefe8bd-5d6f-4038-90e8-05a8277637f0"}, {"$set": {"staff.totalStaff.partTime": 9}})

Example 3 - Create a new field that does not exist

Create a new field called "formerName" with the old name of the store.

db.stores.updateOne({"_id": "8eefe8bd-5d6f-4038-90e8-05a8277637f0"}, {"$set": {"formerName": "Tailwind Traders | Drone Shoppe - New Theodora"}})

Example 4 - Create a new field in a nested object

Create a new field within the nested totalStaff object to specify a count of temporary staff members.

db.stores.updateOne({"_id": "8eefe8bd-5d6f-4038-90e8-05a8277637f0"}, {"$set": {"staff.totalStaff.temporary": 3}})

Example 5 - Update multiple fields

db.stores.updateOne({"_id": "8eefe8bd-5d6f-4038-90e8-05a8277637f0"}, {"$set": {"staff.totalStaff.partTime": 9, "sales.totalSales": 3611}})

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